Lignin, a by-product from the pulp and paper industry is a potentially important chemical to be used in polymer composites. One significant area is epoxy resin and epoxy resin composites for metal coatings.
Metal food and beverage cans have a protective coating on the interior surface, which is essential to prevent the content from coming into contact with the metal surfaces of the containers. Contact of the canned food with the metal surface can lead to corrosion of the metal container and results into contamination and spoiling of food content. In addition, these coatings protect food products from the metal surface to prevent degradation of taste, texture and color.
The most common and important class of epoxy resins utilizes the reaction between Bisphenol-A (BPA) and epichlorohydrin. While it has been demonstrated that epichlorohydrin can be produced from glycerol, a renewable by-product, replacing non-renewable BPA to formulate a completely renewable epoxy resin remains a challenge.
There are major concerns on using epoxy based can coatings based on Bisphenol A (BPA), which is endocrine disrupter. The 2003-2004 National Health and Nutrition Examination Survey (NHANES III) conducted by the Centers for Disease Control and Prevention (CDC) revealed widespread human exposure to BPA from canned food products. It was discovered that there were detectable levels of BPA in 93% of 2517 urine samples from people six years and older. BPA based epoxy coatings for infants and small children food products have been banned by some countries including Denmark, France, Belgium and Sweden.
There is also increasing pressure on coating formulators to phase out BPA based coatings for food contact applications. Currently, the food packaging industry and consumer groups are developing non-BPA interior coatings or have established timetables for replacement of more acceptable substitutes. Owing to the low to-none toxicological effects, great availability and renewability, lignin, with its' aromatic backbone and reactive hydroxyl groups could be a potential substitute for BPA. Taking full advantage of the structural and chemical properties of lignin, it is expected that lignin-based resins can display similar properties to those based on non-renewable petrochemical precursors. Over the years a great number of reports have demonstrated the feasibility of incorporating lignin into epoxy resin formulations. Several approaches have been demonstrated, direct utilization of lignin (J. Appl. Polym. Sci. 42(5), 103-1318, (1991); Holzforschung 51(2), 183-187 (1997); J. Appl. Polym. Sci. 127(3), 1863-1872 (2013)), modification of lignin prior to epoxy resin formulation (Macromol. Chem. Phys. 195(1), 65-80 (1994); Bioresources 6(3), 3515-3525 (2011); Pat. No. US2012148740A1; Pat. No. WO2013050661) and utilization of lignin as a curing agent (Bioresources, 6(4), 5206-5223, (2011) or as a cross-linking agent (U.S. Pat. No. 5,833,883).
Further, U.S. Pat. No. 5,063,089 discloses a metal treatment solution comprising an effective amount of a soluble or dispersible compound which is a derivative of a polyphenol.
Further, DE20202181U1 discloses a vessel for liquid substances which is made from thermoplastic material containing lignin.
In addition, WO2006067229 discloses a vessel, in particular an urn made from a biodegrable material, wherein said material is a starch-free injection moldable material which essentially contains wood fibers and natural fibers and wood powder and binding agents, preferably lignin.
Accordingly there is a need for a solution solving one or more of the above problems.